# Neutronic modeling of a subcritical system with corium particles and water from international benchmark

7/09/2020 2020 - #02 Modelling processes at nuclear facilities

Smirnov A.D. Bogdanova E.V. Pugachev P.A. Saldikov I.S. Ternovykh M.Y. Tikhomirov G.V. Takezawa H. Muramoto T. Nishiyama J. Obara T.

https://doi.org/10.26583/npe.2020.2.12

### UDC: 621.039.58

After the accident at the Fukushima Daiichi nuclear power station, the attention of the scientific community is riveted on how the consequences are being eliminated. Removing corium – a resolidified mixture of nuclear fuel with other structural elements of the reactor – remains the most difficult task, the solution of which can take several decades. It is extremely important to exclude the occurrence of any emergency processes during the removal of corium. The purpose of this work was to solve a coordinated hydrodynamic and neutron-physical problem characterized by a large number of randomly oriented and irregularly located corium particles in water as part of the development of a benchmark for this class of problems. Monte Carlo- based precision codes were used to perform a neutronic analysis. The positions of particles with corium were obtained from the results of numerical simulation. The analysis results obtained using the codes involved showed good consistency for all the states considered. It was shown that modern neutronic codes based on the Monte Carlo method successfully cope with the geometric formation and solution of the problem with a nontrivial distribution of corium particles in water. The results of the study can be used to justify the safety of corium handling procedures, including its extraction from a damaged power unit.

### References

- Robot squeezes suspected nuclear fuel debris in Fukushima reactor. The Verge. Available at: https://www.theverge.com/2019/2/15/18225233/robot-nuclear-fuel-debris-fukushima-reactor-japan (accessed 03.05.2020).
- Baranov V.G., Ternovykh M.Y., Tikhomirov G.V., Khlunov A.V. Simulation of nuclear- physical processes in the surface layer of a fuel kernel with a consumable absorber. At. Energy, 2008, 105 (6), pp. 391-396.
- Kryuchkov E.F., Ternovykh M.Y. Tikhomirov G.V., Li C., Shmelev A.N., Saito M. Deep Burnup High burnup fuel cycles : reactivity coefficients analysis. Izvestiya Wysshikh Uchebnykh Zawedeniy. Yadernaya Energetika, 2004, no. 3, pp. 73-78 (in Russian).
- Albrek M.M., Ternovykh M.Y., Shorov V.Y. Influence of accounting the distribution parameters of the fuel assembly (FA) and dynamic operating characteristics on the fuel nuclide composition of a VVER-1000 spent fuel assembly (SFA). Journal of Physics: Conference Series, 2018, v. 1133, p. 012008.
- Hashlamoun T.M., Vygovsky S.B., Leskin S.T., Duman A.S. Determination of 18-month fuel cycle parameters for the purpose of fuel costs minimization at the basis of use constructions of fuel assemblies in VVER-1200 reactors. Nucl. Energy Technol, 2019, v. 5 (1), pp. 9-15.
- Burnup Credit Criticality Benchmark Phase IIIC – Nuclide Composition and Neutron Multiplication Factor of BWR Spent Fuel Assembly for Burnup Credit and Criticality Control of Damaged Nuclear Fuel. OECD, 2012, 184 p.
- Darnowski P., Potapczyk K., Gatkowski M., Niewinski G. Development of One-way-coupling Methodology between Severe Accident Integral Code MELCOR and Monte Carlo Neutron Transport Code SERPENT. Procedia Eng, 2016, 157, pp. 207-213.
- List of Documents concerning the Response Status at Fukushima Daiichi Nuclear Power Station and Fukushima Daini Nuclear Power Station. TEPCO, 2012, 186 p.
- Burn-up Credit Criticality Safety Benchmark Phase III-c, Tech. Rep. OECD, 2015, 255 p.
- Darnowski P., Potapczyk K., Swirski K. Investigation of the recriticality potential during reflooding phase of Fukushima Daiichi Unit-3 accident. Ann. Nucl. Energy, 2017, 99, pp. 495-509.
- Fernandez-Moguel L., Birchley J. Analysis of the accident in the Fukushima Daiichi nuclear power station Unit 3 with MELCOR_2.1. Ann. Nucl. Energy, 2015, 83, pp. 193-215.
- Freiria Lopez M., Buck M., Starflinger J. A Criticality Evaluation of Fukushima Daiichi Unit 1 Fuel Debris. Volume 9: Student Paper Competition. American Society of Mechanical Engineers, 2018.
- Freiria Lopez M., Buck M., Starflinger J. Neutronic modeling of debris beds for a criticality evaluation. Ann. Nucl. Energy, 2019, v. 130, pp. 164-172.
- Tuya D., Obara T. Supercritical transient analysis in hypothetical fuel-debris systems by multi-region approach based on integral kinetic model. Ann. Nucl. Energy, 2018, 120, pp. 169-177.
- Fukuda K., Tuya D., Nishiyama J., Obara T. Radiation Dose Analysis in Criticality Accident of Fuel Debris in Water. Nucl. Sci. Eng., 2020, v. 194 (3), pp. 181-189.
- Gunji S., Tonoike K., Izawa K., Sono H. Study of experimental core configuration of the modified STACY for measurement of criticality characteristics of fuel debris. Prog. Nucl. Energy, 2017, v. 101, pp. 321-328.
- Chikhi N., Fichot F., Swaidan A. Effect of water entrainment on the coolability of a debris bed surrounded by a by-pass: Integral reflood experiments and modelling. Ann. Nucl. Energy, 2017, v. 110, pp. 418-437.
- Particleworks Europe. Available at: http://www.particleworks-europe.com/ (accessed 03.05.2020).
- Muramoto T., Nishiyama J., Obara T. Numerical analysis of criticality of fuel debris falling in water. Ann. Nucl. Energy, 2019, 131, pp. 112-122.
- Kalugin A.V., Tebin V.V. Criticality Calculations of Non-Оrdinary Systems. VANT. Ser. Fizika Yadernykh Reaktorov. 2015, v. 5, pp. 4-17 (in Russian).
- Oleynik D.S. The Monte Carlo estimation of an effect of uncertainties in initial data on solving the transport equation by means of the MCU code. Phys. At. Nucl. Maik Nauka Interperiodica Publishing. 2015, v. 78 (11), pp. 1194-1199.
- Leppaanen J., Pusa M., Viitanen T., Valtavirta V., Kaltiaisenaho T. The Serpent Monte Carlo code: Status, development and applications in 2013. Ann. Nucl. Energy, 2015, v. 82, pp. 142-150.
- MVP/GMVP version 3: General purpose Monte Carlo codes for neutron and photon transport calculations based on continuous energy and multigroup methods. JAEA, 2017, 446 p.

nuclear safety beyond-design-basis accident nuclear fuel extraction MCU MVP SERPENT